1. Field of the Invention
This invention relates to a photoelectric transducer which photoelectrically converts light information signals to electric signals and sends them out and particularly, to a solid state photoelectric transducer suitable for letter or image input devices such as, for example, a facsimile, digital copier, laser recording device and the like.
2. Description of the Prior Art
Conventional photoelectric transducers comprise a photoelectric transducer element (picture element) group and a circuit having a scanning ability capable of generating electric signals from the photoelectric transducer element subsequently in time sequence.
There are various types of conventional photoelectric transducers such as a transducer containing a photodiode and MOS.FET (Field Effect Transistor) (hereinafter referred to as "MOS type") or a transducer containing a charge transfer device (CTD) such as CCD (Charge coupled device) and BBD (bucket brigade device) (hereinafter referred to as "CTD type") and the like.
However, since the MOS type and the CTD type use a wafer substrate of silicon single crystal (hereinafter referred to as "C-Si"), the area of a light receiving surface of the photoelectric transducer is restricted by the size of the C-Si wafer. At present, there can be produced a C-Si wafer substrate of at most several inches in size only when uniformity all over the region is required. Therefore, in the case of a photoelectric transducer of MOS type or CTD type employing such a C-Si wafer substrate, the area of the light receiving surface can not exceed the area of the C-Si wafer substrate.
Therefore, a photoelectric converting apparatus having a photoelectric transducer with a light receiving surface having such a limited small area requires that an optical system of large reduction magnification should be placed between an original to be reproduced and a light receiving surface so as to form an optical image of the original on the light receiving surface by way of said optical system, for example, when the photoelectric transducer is used as a light information input device for a digital copier.
In such a case as mentioned above, there is a technical limit as to enhancing the resolving power as shown below. That is, assuming that the resolving power at the photoelectric transducer portion is 10 lines per 1 mm, the longitudinal length of the light receiving surface is 3 cm, and the size of the original is "A4", the optical image formed on the light receiving surface is reduced to about 1/69 times the original and the substantial resolution lowers to about 1.5/mm at the photoelectric transducer. In this way, a substantial resolution lowers in proportion to the size of the original to be produced at a rate of (size of the light receiving surface)/(size of the original).
The above mentioned drawbacks may be solved by enhancing the resolution at the photoelectric transducer portion, but for the purpose of obtaining the required resolution when a substrate having such a limited small area as above is used, it is necessary to enhance the integration density to a great extent and produce construction elements free from defects, but such production technique is not so easy.
There has been proposed a system where a plurality of photoelectric transducers are arranged and the ratio of the longitudinal length of the whole light receiving surface to the length in the direction of main scanning of an original of the maximum size to be reproduced is selected as 1:1 and thereby the optical image formed of the original is divided into the number of the photoelectric transducers resulting in prevention of substantial lowering of the resolution.
However, even in such system, there are the following drawbacks. That is, when a plurality of photoelectric transducers are provided, there are inevitably formed boundary regions between photoelectric transducers where any light receiving surface is not present and therefore, as a whole, the light receiving surface becomes non-continuous and the optical images formed are divided and as to the portions corresponding to the boundary regions, no input occurs at the light receiving surface of the photoelectric transducer apparatus and the reproduced images contains white lines at the corresponding portions and are incomplete. Further, the resulting optical images divided into a plurality of light receiving surfaces are optically reversed images at each light receiving surface so that the whole image is different from the optically reversed image of the original. Therefore, when the optical image formed on the light receiving surface is reproduced as it is, it is not possible to reproduce the original.
As mentioned above, the light receiving surface of a conventional photoelectric transducer is so small that it is very difficult to reproduce information at high resolution. Therefore, it is highly demanded that a photoelectric transducer have a long light receiving surface and a high resolving power. In particular, as a photoelectric transducer apparatus used for a light information input device of a facsimile or digital copier, or image reading device for letters or images of an original, a photoelectric transducer apparatus is essential which has a photoelectric transducer having a light receiving surface of almost the same size as that of an original, not lowering the resolution required for the produced image and capable of reproducing an original with high fidelity.